1. Field of the Invention
The present invention relates to a control system for a transmission, and more particularly to a control system fitted to a transmission for marine application in which the output drive shaft is arranged to drive a propeller unit.
2. Description of Related Art
Marine propulsion systems are typically constructed with an engine driving a propeller by means of an intermediate transmission. The transmission may also include one or more coupling means in the form of a clutch that allows for the engagement and disengagement of the transmission with the propeller drive shaft. Such a transmission can be arranged to provide both forward and reverse operation of the propeller drive shaft.
In one arrangement, the engine-driven input shaft of the transmission is permanently connected, by a conical gear coupling, to a pair of opposed conical gears. Each of the gears is also rotatably supported on the transmission output drive shaft so that the opposed conical gears can rotate without being engaged with the transmission output shaft. In order to engage one of the opposed conical gears, each conical gear is arranged with its own fluid clutch. The clutches are engaged by supplying fluid pressure to them. Engagement of a clutch will thus cause either forward or reverse rotation of said transmission output shaft.
When driving a boat or other marine vessel, a problem occurs at low engine speed operation, e.g., at engine tickover speed (which typically lies between 500 to 900 r.p.m.), or at very low engine speed (typically up to about 1,200 r.p.m.). A significant amount of vibration often occurs at these speeds, both in forward and reverse drive modes. Additionally, the forward or reverse movement of the boat may be somewhat uneven.
The present invention reduces or overcomes the aforementioned vibrational problems by the provision of an appropriate control arrangement for the transmission system.